Cell surface receptors for growth factors play a major role in controlling cell division, different tumorigenesis. The avian c-erbB gene encodes a cell surface receptor that is homologous to the human epidermal growth factor receptor; both gene products possess intrinsic tyrosine kinase activity. It is known that mutant c-erbB encoded receptors mediate transformation in avian tissues to produce hemangiomas, fibrosarcomas and eyrthroleukemias. The primary goal of this project is to identify the cellular substrates which mediate c-erbB 1 oncogenesis. The analysis of intracellular substrates which become tyrosine phosphorylated through their interaction with the kinase domain of the c-erbB receptor will be accomplished using antiphosphotyrosine antibodies in conjunction with immunoblotting and immunoaffinity chromatographic techniques. The tissue-specific c-erbB transforming mutants that are available for these experiments win create a powerful and specific method of identifying phosphotyrosine proteins important in mediating c-erbB's oncogenic activity in endothelial, mesenchymal and hematopoietic target tissues. In addition, the production of monoclonal antibodies against phosphotyrosine proteins will allow immunoaffinity purification and further characterization of these substrates. During Phase I of this research plan we propose to generate antiphosphotyrosine antibodies to detect phosphorylated proteins and to identify substrates of the c-erbB encoded tyrosine kinase. During Phase II, we will continue to study signal transduction by c-erbB in the avian system (in which erbb was originally discovered) and will begin to examine human pediatric tumors. Many pediatric tumors are embryonal in nature. Since protein tyrosine kinase play a critical role in embryonal cell growth and differentiation, embryonal kinases and their phosphorylated substrates will be investigated to elucidate the potential role of tyrosine kinases in the development of pediatric tumors. The reagents generated in thc course of these studies (monoclonal antibodies, cDNA probes) may ultimately be useful as diagnostic and/or prognostic indicators in human cancers.